LM80 - What is it?

Light emitting diodes (LEDs) are a relatively new and unique source for lighting.

They are more reliant upon effective thermal management than any previous source, and have to be designed and tested as an entire lighting system. Therefore, LEDs require new guidelines and practices for testing. There also needs to be a correlation between how LED manufacturers test their LEDs and how fixture manufacturers test their LED fixtures. In response, the Illuminating Engineering Society of North America

or IESNA developed several testing procedures, one of which is LM-80.

Since LEDs are solid state and directly convert electricity to light, their lumen maintenance is better than traditional sources. Lumen maintenance is a measure of how well a light source maintains its lumen output over time, typically shown as a percentage of initial light output. Typical LED lumen maintenance is 70% for 50,000+ hours – a marked improvement over traditional sources.  70% lumen maintenance means the LEDs will still produce 70% of their initial light output, or only 30% lumen degradation. Research shows also that reductions to 70% of initial light output are considered acceptable by the majority of occupants within a space.

LM-80 Approved Method: Measuring Lumen Maintenance of LED Light Sources was

published by the IESNA Solid State Lighting (SSL) Subcommittee in the third quarter of

2008. This document covers lumen maintenance measurement for inorganic LED-based packages, arrays, and modules3; it does not cover any other aspect of LED performance.

One of the key reasons for the development of LM-80 is due to differences in measuring

LED performance criteria. LED manufacturers manufacturers measure their products deifferently from LED fixture manufactures. Typically a LED manuf. will measure LEDs in pulse mode operation with no heat sink. The pulse is very short – typically 10 or 20 milliseconds (that is, thousandths of a second) – which will not heat up the LED; therefore, no heat sink is required and temperature can be assumed to be equal to ambient temperature. In contrast, LED fixture manufacturers measure LED performance in situ, which means while it is in their fixture. Under these conditions, the LED is operated in constant DC mode and there are typically numerous LEDs configured together often in close proximity to one another, elevating temperature. This elevated temperature affects the photometric and colorimetric performance of the LEDs. In order to compare “apples to apples”, a new testing criteria needed to be developed – enter LM-80.

LM-80 prescribes uniform test methods for LED manufacturers under controlled conditions for measuring LED lumen maintenance while controlling the LED’s temperature.

Based upon LM-80 data, LED manufacturers then extrapolate lumen maintenance out to tens of thousands of hours.  While LM-80 does not specify the extrapolation method, many LED manufacturers use more conservative exponential extrapolation due to the exponential behavior of LEDs and most electronic components. The SSL Subcommittee is working on TM-21 which will standardize this extrapolation method.